Patient couches in C-arm computed tomography systems are generally realized such that certain body parts can be imaged with little effort, in particular without a considerable movement of the couch from its standard position. This is the case for example when imaging the spinal column. In contrast when imaging certain organs, allowance must be made for the position of these organs within the patient's body. For example if the liver of a patient is to be imaged, the couch must be brought to a defined position such that the isocenter of the C-arm of the C-arm computed tomography system coincides directly in the liver. Achieving this state is not very straightforward. Usually an operator, who is frequently the doctor performing the treatment, has to displace the couch by hand and thereby attempt to guess the optimal position as far as possible, and then gradually reach that position by trial and error. This method is time-consuming and the doctor performing the treatment possibly has to capture a fairly large number of x-ray images (so-called projections) in order to correct the current position of the couch with the aid of a view of the area of the patient that is of interest in the x-ray images.
U.S. Pat. No. 6,309,103 B1 describes an x-ray imaging device with independent movement apparatuses for the patient couch on the one hand and for an x-ray radiation source and an x-ray radiation detector on the other hand, with the latter together being rotatable about the patient. The x-ray images of the patient are displayed on a screen. Using a computer mouse the doctor can then select the area of the patient that he wishes to examine.
The device furthermore has a calculating unit which, on the basis of at least two images of the patient captured by the x-ray device from two different directions, calculates the position of the area being observed in relation to the center of rotation of the x-ray radiation source and the x-ray radiation detector. It further consists of a control unit by means of which the movement apparatuses can be controlled.
The publication DE 10 2005 059 804 A1 discloses an image correction method for imaging during a medical intervention. A tomographic 3D image of a target area of the intervention is recorded while one or several medical instruments are located in the target area. These instruments remain in the target area during the intervention, and 2D x-ray images of the target area are recorded and registered with the 3D image, with the 2D/3D registration being adjusted in real time for each 2D image. The 2D images are then each overlaid with views of the 3D image that match up from a perspective view.